There are two commonly known types of tree harvesters: single-grip harvesters and double-grip harvesters.
Single-grip harvesters have all their tree processing devices mounted on a single articulated boom. Such an harvester is disclosed in the U.S. Pat. No. 4,416,311, entitled "Tree Harvester", issued on Nov. 22, 1983 and naming Gemmell-Murdoch as inventor. Gemmell-Murdoch's harvester has a felling assembly and a delimbing assembly mounted on the same boom.
A drawback of Gemmell-Murdoch's harvester is that the boom is not available to process another tree or even to be repositioned to process another tree after the felling, since the boom is also used to delimb the tree. Furthermore, since the delimbing assembly is positioned on the boom, single-grip harvester's boom are usually heavy end bulky and can cause damages to the trees. Single-grip harvesters are therefore not particularly efficient.
On the other hand, double-grip harvesters have only their tree felling device mounted to the boom. The other tree processing devices are mounted on a worktable. An example of a double-grip harvester can be found in U.S. Pat. No. 3,805,859, entitled "Delimbing Assembly for a Tree Harvester" and issued to Kessler et al. on Apr. 23, 1974. Kessler's tree harvesting vehicle comprises a tree delimbing assembly mounted in front of the vehicle and an articulated boom that includes a tree felling assembly. After felling a tree, the boom brings the tree to the delimbing assembly. During the delimbing process, the boom can fell a second tree, therefore increasing the overall efficiency of the harvesting vehicle.
A drawback of Kessler's harvester is that the delimbing assembly is fixedly mounted to the vehicle. Indeed, the processed tree sometimes prevents free movement of the boom. Another drawback of Kessler's harvester is that it cannot accumulate trees after the delimbing process. The operation of the boom is therefore often stopped, since the boom has to remove the delimbed tree from the delimbing assembly.
A solution has been proposed to this problem by Hahn in U.S. Pat. No. 4,382,457, issued on May 10, 1983 and entitled "Tree Harvester". Hanh proposes a tree harvester provided with a bed, to delimb and cut a tree to a desired length, and a kickout table to receive and stack the severed logs. While Hahn's machine shows improvements over Kessler's, it presents the major drawback of being huge. This is a major drawback since the bigger the harvester and the greater the chance to damage the trees or the environment. Furthermore, Hahn's machine still has the same problem as Kessler's harvester regarding the fact that, the bed being fixedly mounted to the movable frame, it can sometimes prevent free motion of the boom.